Process for the operation of blast furnaces



United States Patent 3,151,974 RUCESS FGR THE GTERATTGN @F ELAT FURNACESPaul Rheinliinder, Wolfenhuttel, Germany, assignor to HuttenwerkSalzgitter Ahtiengeselischaft, Saizgitter- Drutte, Germany, a Germancompany No Drawing. Filed Apr. 24, 1962, Ser. No. 189,63 Claimspriority, application Germany, Apr. 26, i nl,

H 42,414; Apr. 9, 1962, H 45,415

8 Claims. (Cl. 754-2) Attempts have repeatedly been made to supply someof the carbon necessary for reduction and heat economy in blast furnacesby the injection of solid, liquid and gaseous fuels into the furnacehearth, thus not only saving coke but also replacing it by a fuel whichdoes not occupy furnace space, is simple to convey and, in some cases,is cheaper than coke. These attempts have been completely or partiallyunsuccessful so that the idea has not been adopted in practice. Solid,liquid or gaseous fuels introduced into a blast furnace hearth throughthe tuyeres have a cooling effect on the hearth coke, where it is at amaximum temperature, and this is so even if such fuels are introducedwith a blast of a higher temperature than otherwise conventional.Furthermore, the combustion zone situated in front of the blast furnacetuyeres does not have the oxygen required for the complete combustion ofsuch fuels.

When solid coal dust is injected together with the blast air, the heatrequired to convert the coal dust ash into slag is taken from thetemperature-sensitive hearth of the blast furnace, while when liquid orgaseous hydrocarbons are injected, for example petroleum, petroleumproducts, natural gas, or the like, the heat required for theendothermic cracking process has to be supplied at the blast furnacehearth. These functions additionally constitute a load on the furnacehearth because the supply of fuels is not always uniform, but isfrequently possible only with fluctuations per unit of time, as a resultof the furnace operation.

The object of the invention is to replace some of the cok charged at theblast furnace throat, by liquid or gaseous hydrocarbons, in the form ofpetroleum, petro leum products or natural gas. To solve this ditficultproblem, according to the invention, the petroleum products or naturalgas are not introduced as such together with the blast air into theblast-furnace hearth, as was previously the case, but instead they arecracked and the cracked products comprising soot, hydrogen, carbondioxide and nitrogen are then introduced into the furnace. It ispreferable to inject into the blast furnace hearth together with the hotblast air the soot originating from the cracking and to use only a smallfraction of the cracked gases as a carrier gas. The major part of thecracked gas consisting substantially of hydrogen, carbon monoxide andnitrogen, is then introduced into the furnace boshes or shaft, Where ithas a reducing or heating action. The introduction may take place in thezone of the shaft in which heat is additionally required due to theexpulsion of carbon dioxide from the ores. The soot blown into thefurnace hearth together with the blast air through the tuyeres isreadily combustible at a low ignition temperature. No ash has to beconverted into slag as is the case with coal dust.

Surplus cracked gas consisting mainly of hydrogen and carbon monoxideand nitrogen may also be used as longdistance gas or town gas. In thatcase, it is previously brought to long-distmce gas or town gas densityand calorific value by mixing it with a supplementary gas, for example,natural gas. The cracked gas has a density of about 0.329 (referred toair l) and a top calorific value of 2460 kilogram calories per cubicmeter. By the addition of 0.08 cu. meter of blast-furnace gas (density1.02,

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calorific value 900 kilogram calories per cubic meter) and 0.38 cubicmeter of natural gas (density 0.67, calorific value 11,100), to eachcubic meter of cracked gas a long-distance or town gas is obtained witha density of 0.455 and a top calorific value of 4620 kilogram caloriesper cubic meter.

The cracking process which precedes the introduction into the blastfurnace can be performed particularly advantageously in regenerativechambers equipped with a ceramic lattice. Two pairs of chambers, i.e.,four regenerative chambers, are required for a continuous crackingoperation. While heating up takes place in two of these chambers, thechambers heated by blast-furnace throat gas or by fuel oil to about 1400C., the cracking process takes place in the second pair of chamberswhich have previously been heated to 1400 C. To bring about the crackingair is heated to about 1300 to 1400 C. in the first of the pair ofchambers, and oil is injected into the hot air leaving the chamber, theamount of oil being approximately 2.5 metric tons per 1,000 cubicmeters. The quantity of air in relation to the quantity of oil injectedis so small that the oil is only extremely incompletely burned in thesecond of the pair of chambers and is cracked there into soot and a gasconsisting mainly of hydrogen, carbon monoxide and nitrogen. One metricton of oil gives about 800 kg. of soot and 1700 cubic meters of crackedgas containing 71% H 10% Co and 19% N The heat stored in the crackingchamber lattice during the heating-up period furnishes the energyrequired for the cracking process, so that the cracked products retainthe temperature to which the hot air required for cracking waspreviously heated. When the cracked product temperature has dropped toabout 1200 C., the regenerative chambers are switched over. The firstpair of chambers which were hitherto undergoing heating-up only, nowserve for air heating and cracking, while the second pair of chambers isheated with blast furnace throat gas or fuel oil again to a temperatureof about 1400" C.

After leaving the regenerative chambers the cracked products enter acyclone in which the soot and the cracked gas are separated from oneanother. The cracked gas can all be used in the blast furnaces, namelyin the boshes or shaft as a reducing or heating agent, or alternatively,part of the gas after appropriate preparation, can be used aslong-distance or town gas. A small proportion of the cracked gasaccumulating in the cyclone is utilized for the conveyance of the sootfrom the cyclone to the blast furnace tuyeres.

It is advantageous not to introduce the soot from the cyclone directlyinto the blast-furnace hearth, but to conduct it into a reservoircontainer from which it is then injected into the hot air by some of thecracked gas and blown together with the blast air into the blast-furnacehearth. The storage of soot in the reservoir renders the crackingoperation independent of the blast furnace operation, so that nointerruptions are necessary, for example, in the event of blast-furnacedisturbances.

Instead of performing the cracking process in regenerative chambersfollowed by a cyclone, it may also be performed entirely in a cyclone.In this case hot air is injected into the cyclone through the inletwhich leads tangentially into the cyclone, the hot air preferably beingtapped from the blast-furnace blast pipe, and oil is injected into thehot stream of air. The ratio of hot air to oil is again so adjusted thatthe oil undergoes only extremely incomplete combustion in the cycloneand is cracked into soot and cracked gas. The hot air serving forcracking may also be oxygen-enriched. The soot accumulating in thecyclone emerges from the bottom end of the cyclone together with a smallproportion of cracked gas. It is preferably again fed to a storagecontainer fol lowing the cyclone, and is introduced from the containerwith a little of the cracked gas serving as carrier gas, together withthe blast-furnace blast air, into the furnace hearth. The major portionof the cracked gas leaves the cyclone at the top end. It is blown intothe blast-furnace boshes or shaft or part of it is used as long-distanceor town gas after being enriched, for example, by means of natural gas.

Instead of performing the cracking process in a single cyclone, it maybe performed in a number of individual cyclones which are then soconnected to the blast-furnace tuyeres that the soot emerging from thebottom end of the cyclone passes directly into the nozzles and blast-airof the furnace. Such individual cyclones may also be replaced by oilburners preceding the blast-furnace tuyeres, particularly tangentialburners.

The cracking process can be conveniently controlled in hot cyclones ofthe kind described, for example by producing varying amounts of soot byvarying the ratio of hot air and oil, and thus adapting the supply offuel to the blast-furnace hearth to the furnace operation.

Finally, some of the petroleum products may be cracked in the top partof the blast-furnace shaft. The heatconsuming cracking process thentakes place at the expense of the perceptible heat of the blast-furnacegas ascending in the furnace shaft. The throat gas temperature isdiminished in these conditions and reduction takes place. The crackedgas calorific value can then be used together with the throat gas.

The introduction of the cracked gases resulting from the cracking ofliquid or gaseous hydrocarbons, into the blast furnace, lowers thepartial pressure of the hydrogen contained in the blast furnace gas andincreases that of the reducing gas constituents, for example, the carbonmonoxide and hydrogen. This results in an increase in the amount ofindirect reduction and a lowering of the coke consumption.

I claim:

1. In a process for the operation of a blast furnace wherein part of thecoke charged at the throat of the furnace is replaced by hydrocarbonmaterials selected from the group consisting of petroleum and naturalgas which are cracked outside the furnace and then introduced therein inthe form of soot and a gaseous product comprising hydrogen, carbonmonoxide and nitrogen, the steps which comprise cracking said materialsby an incomplete combustion with hot air to obtain a maximum amount ofsoot, the ratio being approximately 2.5

the group consisting of petroleum and natural gas which are crackedoutside the furnace and then introduced therein in the form of soot anda gaseous product comprising hydrogen, carbon monoxide and nitrogen, thesteps which comprise cracking said materials by an incomplete combustionwith hot air to obtain a maximum amount of soot, tapping said air fromthe supply of blast air to the furnace, the ratio being approximately2.5 metric tons hydrocarbons to 1,000 in. air; separating said soot fromthe gaseous products obtained by said cracking; separating said gaseousproducts into a small fraction and a relatively larger, major, fraction;entraining said soot in said small fraction; injecting said smallfraction .and its entrained soot into the furnace hearth; andintroducing said larger fraction into said blast furnace above thehearth thereof.

3. In a process for the operation of. a blastfurnace wherein part of thecoke charged at the throat of the furnace is replaced by hydrocarbonmaterials selected from the group consisting of petroleum and naturalgas which are cracked outside the furnace and then introduced therein inthe form of soot and a gaseous product comprising hydrogen, carbonmonoxide and nitrogen, the steps which comprise cracking said materialsby an incomplete combustion with hot air in a central cyclone precedingthe blast furnace to obtain a maximum amount of soot, the ratio beingapproximately 2.5 metric tons hydrocarbons to 1,000 in. air; separatingsaid soot from the gaseous products obtained by said cracking;separating said gaseous products into a small fraction and a relativelylarger, major, fraction; entraining said soot in said small fraction;injecting said small fraction and its entrained soot into the furnacehearth; and introducing said larger fraction into the blast furnaceabove the hearth thereof.

4. In a process for the operation of a blast furnace wherein pant of thecoke charged at the throat of the furnace is replaced by hydrocarbonmaterials selected from the group consisting of petroleum and naturalgas which are cracked outside the furnace and then introduced therein inthe form of soot and a gaseous product comprising hydrogen, carbonmonoxide and nitrogen, the steps which comprise cracking said materialsby an incomplete combustion with hot air in individual cyclonespreceding the blast furnace tuyeres to obtain a maximum amount of soot,the ratio being approximately 2.5 metric tons hydrocarbons to 1,000 m.air; separating said soot from the gaseous products obtained by saidcracking; separating said gaseous products into a small fraction and arelatively larger, major, fraction; entraining said soot in said smallfraction; injecting said small fraction and its entrained soot into thefurnace hearth; and introducing said larger fraction into the blastfurnace above the hearth thereof.

5. In a process for the operation of a blast furnace wherein part of thecoke charged at the throat of the furnace is replaced by hydrocarbonmaterials selected from the group consisting of petroleum and naturalgas which are cracked outside the furnace and then introduced therein inthe form of soot and a gaseous product comrising hydrogen, carbonmonoxide and nitrogen, the steps which comprise cracking said materials,to obtain a maximum amount of soot, in two series-connected regenerativechambers heated to approximately 1,400 C.; heating air to 1,3001,400 C.in the first of said two heated chambers; passing said heated air intothe second heated chamber; injecting said hydrocarbons into said heatedair in the second chamber, the ratio being approximately 2.5 metric tonshydrocarbons to 1,000 m. air; cracking said hydrocarbons by said hot airin said second chamber; separating in a cyclone said soot from thegaseons products obtained by crack-ing; separating said gaseous productsinto a small fraction and a relatively larger, major, fraction;entraining said soot in said small fraction; injecting said smallfraction and its entrained soot into the furnace hearth; and introducingsaid larger fraction into the furnace above the hearth thereof.

6. In a process for the operation of a blast furnace wherein part of thecoke charged at the throat of the furnace is replaced by hydrocarbonmaterials selected from the group consisting of petroleum and naturalgas which are cracked outside the furnace and then introduced therein inthe form of soot and a gaseous product comprising hydrogen, carbonmonoxide and nitrogen, the steps which comprise cracking said materialsby an incomplete combustion with hot air to obtain a maximum amount ofsoot, the ratio being approximately 2.5 metric tons hydrocarbons to1,000 m. air; separating said soot from the gaseous products obtained bycracking in a cyclone; storing the soot in a container following saidcyclone; separating said gaseous products into a small fraction and arelatively larger, major, fraction; entraining l :59 said soot in saidsmall fraction; injecting said small fraction and its entrained sootinto the furnace hearth; and introducing said larger fraction into thefurnace above the hearth thereof.

7. In a process for the operation of a blast furnace wherein part of thecoke charged at the throat of the furnace is replaced by hydrocarbonmaterials selected from the group consisting of petroleum and naturalgas Which are cracked outside the furnace and then introduced therein inthe form of soot and a gaseous product comprising hydrogen, carbonmonoxide and nitrogen, the steps Which comprise cracking said materialsby an incomplete combustion to obtain a maximum amount of soot, theratio being approximately 2.5 metric tons hydrocarbons to 1,000 m. air;separating said soot from the gaseous products obtained by saidcracking; separating said gaseous products into a small fraction and arelatively larger, major, fraction; entraining said soot in said smallfraction; injecting said small fraction and its entrained soot into thefurnace hearth; and introducing said larger fraction, While hot, intosaid blast furnace above the hearth thereof.

8. In a process for the operation of a blast furnace wherein part of thecoke charged at the throat of the furnace is replaced by hydrocarbonmaterials selected from the group consisting of petroleum and naturalgas which are cracked outside the furnace and then introduced therein inthe form of soot and a gaseous product comprising hydrogen, carbonmonoxide and nitrogen, the steps which comprise cracking said materialsby an incomplete combustion With hot air to obtain a maximum amount ofsoot, the ratio being approximately 2.5 metric tons hydrocarbons to1,000 m. air; separating said soot from the gaseous products obtained bysaid cracking; separating said gaseous products into a small fractionand a relatively larger, major, fraction; entraining said soot in saidsmall fraction; injecting said small fraction and its entrained sootinto the furnace hearth; introducing part of said larger fraction intosaid blast furnace above the hearth thereof; adding to the remainder ofsaid larger fraction blast furnace gas and natural gas to obtain desireddensity and calorific value; and burning the resulting mixture to meetexternal fuel requirements.

References ited in the file of this patent UNITED STATES PATENTS1,349,598 Basset Aug. 17, 1920 1,872,900 Crocker Aug. 23, 1932 2,420,398Kinney May 13, 1947 2,719,083 Pomykala Sept. 27, 1955 2,833,643 NewmanMay 6, 1958 2,952,533 Cuscoleca Sept. 13, 1960

1. IN A PROCESS FOR THE OPERATION OF A BLASTD FURNACE WHEREIN PART OFTHE COKE CHARGED AT THE THROAT OF THE FURNACE IS REPLACED BY HYDROCARBONMATERIALS SELECTED FROM THE GROUP CONSISTING OF PETROLEUM AND NATURALGAS WHICH ARE CRACKED OUTSIDE THE FURNACE NAND THEN INTRODUCED THEREININ FORM OF SOOT AND A GASEOUS PRODUCT COMPRISING HYDROGEN, CARBONMONOXIDE AND NITROGEN, THE STEPS WHICH COMPRISE CRACKING SAID MATERIALSBY AN INCOMPLETE COMBUSTION WITH HOT AIR TO OBTAIN A MAXIMUM AMOUNT OFSOOT, THE RATIO BEING APPROXIMATELY 2.5 METRIC TONS HYDROCARBONS TO1,000 M.3 AIR; SEPARATING SAID SOOT FROM THE GASEOUS PRODUCTS OBTAINEDBY SAID CRACKING; SEPARATING SAID GASEOUS PRODUCTS INTO A SMALL FRACTIONAND A RELATIVELY LARGER, MAJOR, FRACTION; ENTRAINING SAID SOOT IN SAIDSMALL FRACTION; INJECTING SAID SMALL FRACTION AND ITS ENTRAINED SOOTINTO THE FURNACE HEARTH; AND INTRODUCING SAID LARGER FRACTION INTO SAIDBLAST FURNACE ABOVE THE HEARTH THEREOF.